1. Field of the Invention
The present invention relates to a semiconductor light-emitting device using a nitride based compound semiconductor material, and more particularly, to a nitride based compound semiconductor light-emitting device comprising a nitride based compound semiconductor such as GaN, AlGaN and InGaN, and a method for producing the same.
2. Description of the Related Art
In recent years, a semiconductor laser is used in various fields such as home electric products, office automation equipments, communication equipments and industrial measuring instruments. Among them, it is desired to develop a semiconductor laser of short wavelength on purpose to apply it to a high density laser disk recording system which is expected to be used in various field. At the present, a red light-emitting semiconductor laser is used, and its recording density is enhanced as compared with that of a conventional infrared semiconductor laser. However, it is difficult to apply the red light-emitting semiconductor laser to a laser disk recording of the next generation, since there exist a large number of problems concerning the nature of the materials such as crystal defects and the high operating voltage. Further, the oscillation wavelength is about 460 nm at the shortest and thus, it is difficult, in view of physical properties, to let the laser oscillate in a range between 420 nm and 430 nm.
As to nitride based compound semiconductor laser including GaN, it is possible, in principle, to shorten a wavelength down to 350 nm or less, oscillating operation at 400 nm has been reported. Concerning reliability also, it has been confirmed that the nitride based compound semiconductor device was reliably used for more than 10,000 hours as a light-emitting diode(LED). As described above, the nitride semiconductor system is a material having excellent properties that can meet necessary conditions as a laser disk recording laser source of the next generation.
A resonator is required for laser oscillating operation. A usual semiconductor laser has a pair of mirrors consisting of a natural cleavage surface to form the resonator. This utilizes a fact that there exists a plane of smaller bonding energy in a direction of [011] or [0-11] in zincblende(sphalerite) structure of cubic system type, i.e., a cleavage plane. In the nitride semiconductor system, there exist cubic system type and hexagonal system type. At the present, the hexagonal system type crystal grown on a sapphire substrate is the best crystal. However, because the hexagonal system type does not have clear mode of a natural cleavage, the nitride semiconductor crystals are induced to the cleavage plane of the sapphire substrate and broken in such a direction, thus, it is difficult to form the resonant mirrors, causing a problem that the yield of device production process is low.
Further, there is a problem that the resonant mirrors are suddenly deteriorated at the time of operation with high optical output, and problems have been pointed out that a deformation is generated between the resonant mirrors and a substrate due to a heat generated at the time of operation and thus dislocations are increased to deteriorate the mirror surfaces.
Furthermore, when the laser is used as a optical source of the laser recording disk, it is necessary to control a lateral mode and oscillate the laser only by a fundamental mode in order to focus the beam spot thereof. However, controlling the lateral mode in the laser of high output is difficult, especially in the case of the high power lasers for the data writing in the laser disc system.
As described above, in the conventional nitride based semiconductor light-emitting device, there are various problems that it is very difficult to form the resonant mirrors, its reliability is low and the lateral mode control is difficult.